1. Field
The field relates to an organic light emitting display and a driving method thereof, and more particular to an organic light emitting display and a driving method thereof, which may display images of uniform luminance regardless of degradation of an organic light emitting diode and a threshold voltage and/or mobility of a drive transistor.
2. Discussion of Related Technology
Recently, various flat plate displays having reduced weight and volume when compared to cathode ray tubes (CRT) have been developed. Flat panel displays may take the form of liquid crystal displays (LCD), field emission displays (FED), plasma display panels (PDP), and organic light emitting displays.
Among the flat panel displays, the organic light emitting displays make use of organic light emitting diodes that emit light by re-combination of electrons and holes. The organic light emitting display has advantages of high response speed and small power consumption.
FIG. 1 is a circuit diagram showing a pixel 4 of a conventional organic light emitting display.
With reference to FIG. 1, the pixel 4 includes an organic light emitting diode OLED and a pixel circuit 2. The pixel circuit 2 is coupled to a data line Dm and a scan line Sn, and controls the organic light emitting diode OLED.
An anode electrode of the organic light emitting diode OLED is coupled to pixel circuit 2, and a cathode electrode thereof is coupled to a second power supply ELVSS. The organic light emitting diode OLED generates light of a luminance corresponding to an electric current from the pixel circuit 2.
When a scan signal is supplied to the scan line Sn, the pixel circuit 2 controls an amount of an electric current provided to the organic light emitting diode OLED according to a data signal provided to the data line Dm. So as to do this, the pixel circuit 2 includes a second transistor M2, a first transistor M1, and a storage capacitor Cst. The second transistor M2 is coupled between a first power supply ELVDD and the organic light emitting diode OLED. The first transistor M1 is coupled between the data line Dm and the scan line Sn. The storage capacitor Cst is coupled between a gate electrode and a first electrode of the second transistor M2.
The gate electrode of the first transistor M1 is coupled to the scan line Sn, and a first electrode thereof is coupled to the data line Dm. A second electrode of the first transistor M1 is coupled with one terminal of the storage capacitor Cst. Here, the first electrode is a source electrode or a drain electrode, and the second electrode is the electrode different from the first electrode. For example, when the first electrode is the source electrode, the second electrode is the drain electrode. When supplied with a scan signal, the first transistor M1 coupled with the scan line Sn and the data line Dm is turned-on to provide a data signal from the data line Dm to the storage capacitor Cst. The storage capacitor Cst is then charged with a voltage corresponding to the data signal.
The gate electrode of the second transistor M2 is coupled to one terminal of the storage capacitor Cst, and a first electrode thereof is coupled to another terminal of the storage capacitor Cst and a first power supply ELVDD. Further, a second electrode of the second transistor M2 is coupled with an anode electrode of the organic light emitting diode OLED. The second transistor M2 controls an electric current flowing from the first power supply ELVDD to a second power supply ELVSS through the organic light emitting diode OLED according to the voltage charged in the storage capacitor Cst. Here, the organic light emitting diode OLED generates light corresponding to the electric current supplied from the second transistor M2.
The conventional organic light emitting display can not display the images of desired luminance due to degradation of the organic light emitting diode OLED. In practice, as time goes by, the organic light emitting diode OLED is degraded, and accordingly light of lower luminance is gradually generated despite the same data signal. Additionally, the images of desired luminance can not be conventionally displayed due to a non-uniformity of the threshold voltage of the drive transistor M2 in each of the pixels.